Automatic telephone system



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i Y w22/844 May 10 1927 H.^M. FRIENDLY AUTOMATI C TELEPHONE SYSTEMorigina] Filed'Feb. 17. 19 21 9 shams-sheet4 9 @Gunn lll] [l PatentedMay 10,v i927.

stares lltttd HERBERT IVI. FRIENDLY, OF CHICAGO, ILLINOIS.

.AUTOMATIC TELEPHONE SYSTEM.

Application tiled February 1'?, 1921, Serial No.` 445,761.` RenewedNovember 8, 1926.

The present invention relates in general to an automatic telephonesystem, andis particularly adapted to a system that includes a `mainexchange, having a plurality of branch offices tributary to it.

More specifically, the invention relates to an improved method andapparatus for permitting either'a calling party in the main exchange ora called subscriber ina branch exchange lto transfer the call ltoanotherdesired subscriber in the branch exchange. thersystemshave beeninventedwhich em .body certainl arrangements of this nature, rbut hereinare provided many new features together with improvements in thestructure of such a system.

Among the important features of the invention an arrangement is providedwhereby, after a call has been transferred from one `branch exchangesubscriber to another the three parties may remain on the line `for aconference,rand as soon'as this is terminated either party'at the branchexchange may release the other by dialing the digit 1; or should thisfeature not be desirable the first called party may be automaticallyreleased upon the second called party an-V swering.

Another important feature is the provision of means whereby if thebranch rexchange subscriber upon receiving a call should desire toobtain information from another subscriber in the branch exchangewithout the knowledge of the calling party he may do so by dialing thecalling man on t-o a holding circuit,` after which the called party mayrelease and call normally in the branch exchange or into the rvmainexchange; yafter obtaining the information desired, the calledsubscriber may again connect with the original calling subscriber andsubsequently pass or transfer the calls as in the ordinary operation ofthe system.

Means are also provided whereby cert-ain (or all)-branch exchangesubscribers may have special services of an operator if they so desire.

These and other features of the invention will be fully disclosedhereinafter.

Referring now yto the drawings:

Fic. 1 shows a schematic trunkino` dia-l gram of the system disclosed inlthe remaining drawings. i

Fig. 1a shows the manner in which the different sheets of drawings areplaced for a complete view ofthe system.

In F ig. 2 the apparatus at the lmain exchange is shown diagrammaticallyand consists of a subscribers substation A, having a preselector -orrotary lineswitch C5 individual thereto,-and which has access in commonlwith a lplurality of other similar lineswitches to lfirst selectors ofthe standard Keith-Erickson two wire class, one of which is shown'at4 E.These selectors have access to selector repeaters off a vcertain 'levelof bank contacts. The selector repeaters may be of lany well known .twowire rtype such as that shown in Fig. 1 of the 4patent to Emil JacobsenNo. 1,332,217, issued March 2, 1920. These selector repeaters haveaccess to trunk lines going to branch exchanges one of these is shown inthe drawings and vcomprising the conductors 26 and 27.

These trunk lines terminate in what is known as dual selector switchesin the branch exchanges. The switches are of the 'general type shown inFigs. 9 and 10 of the British .patent to Friendly 139,000 the circuitsofwhich are modified in accordance with the features of the presentinvention. The trunk `line comprising conductors 26 and 27 Vis shownterminating in such adual switch, Figs. 3 and 4.

In Figs. 5, 6, 11 and'13 ordinary selector switches of the KeithErickson two wire type are shown, the circuits of which have beenvmodified to operate in this system.

Figs. 7, 8, and 9 show connector switches of the well known Strowgertype which also have been modified as will appear fully hereinafter.

Fig. 10, shows an improvement that has been designed for controlling alarge number of otl normal springs when the weight of the switch shaftis inadequate to shift them.

Fig. 12 shows an operator-s cord-pair.

Figs. 14 and 15 show certain details of the present invention which willbe described fully hereinafter. l

Vhile in the drawings a plurality of batteries have been shownyit willbe understood that there vis perferably, but one battery having itsnegative pole grounded for each exchange.

rlhe operation of this improved system will now `be described ingeneral, reference being had to Fig. 1.

Let us Consider first what is shown on the left of the dotted line,where is `indicated the apparatus in the main exchange. The

. these selector switches terminate selector repeaters one ot which isshown immediately to the right ot the. first selector. Another level oithe selector switches has access to local second selectors showndiagrammatically at the bottom square on the lett; and as` shown onelevel of these selectors go to local connectors which have access tomain exchange subscribers lines. The selector repeaters have access totrunk lines going to the branch exchanges andY termimiting there in dualselectors, one ot' which is shown terminating in the dual selectorswitches in the branch exchange. The switches in the branch exchangeshown on the right of the dotted line consist ot two groups, those usedin a local call and those used .in an incoming call. The dual incomingselectors have access to incoming second selectors off` certain levelsof their bank contacts. These second selectors have access to incomingconnectors which are adapted to connect with local subscribers lines.The local subscribers, shown at upper extremity of the drawing, haveeach an individual rotary line switch which has access to local branchexchange tiret selectors. A certain level of these selectors, the secondas shown, is multipled into the second level of the incoming dualselectors, this is for a special purpose as will later appear. Otherlevels have access to local second selectors, while the 0 level is usedfor outgoing callsI to the main exchange.

The process of setting up connections will now be briefly considered.Suppose vfirst thata subscriber in. main exchange wishes to connect withal subscriber in the branch. exchange. lhen the receiver is removed atthe calling station the rotary line switch in dividual thereto operatesto select an idle first selector. The callingI subscriber' willthereupon dial the digit. which corresponds to the level leading to theselector repeater and which in this case is the digit 7. Then this digitis called the selector steps to the seventh level and operates toautomatically select an idle selector repeater. The calling subscribermay now call the digit 6 whereupon the selector re eater will operatevertically to the sixth evel and rotate to lind an idle trunk line goingto the branch exchange and terminating there in a dual selector. Thecalling party may now call the remaining :tour digits ot the desiredbranch exchange subscribers number whereupon the connection will becompleted `in the usual manner. lt' 1t should be found, upon the calledsubscriber answering, that ari-g .may be again passed, if necessary, asmany si' times as desirable.

Let us consider also the case of where the called party .desires tocommunicate with another subscriber in the branch exchange. He will dialthe digit 2 which will cause the other dual selector element to step tothe 'second level and connect with the holdingr trunk which is multipledinto the second level of the local branch exchange first selectors. Thecalled subscriber may now rclease the connection to himself and use thelocal branch exchange switches to call another party. After obtainingwhatever information he desires he may dial the digit 2 which will causethe local first selector to step tothe second level and then rotate intoconnection with the holding trunk. The called party is now incommunication with the original calling party again and the call may bepassed as in the case first mentioned.

The local branch exchange subscribers by dialing O operate a firstselector vertically to the tenth level whereu on the switchautomatically rotates to fin an idle .two way trunk going to the mainexchange. As soon as this is found the line switch associated therewithin the main exchange oper ates to select an idle first selector'whereafter the call is completed in the usual man ner to a main exchangesubscriber.

Special service is also provided for cer` tain subscribers in the branchexchange. By .removing their receivers and dialing l the first selectorunder their control is stepped to the first level and automaticallyrotated. This action serves to light a line lamp before an operator whocan now res-'pond and set up a connection `troni the calling line eithermanually or automatically in a well known manner. y

Having described the general objects ot' this invention and the generalmanner ot' obtaining these objects. the detailed operation of a systemembodying those improvements will no'w be considered.

For this purpose it will be assumed that a subscriber at substation A inthe main exchange desires to call the branch exchange subscriberatsubstation P and that the said calling subscriber has, by operating hiscall lili] inceneririiig dev-ice vtor a vseries ot digits seized the twoway trunk .line comprising conductors 2G and .27 by .ineaiiso't'thefselector repeater C, in la iwell flinown manner.

lVhen the .call 4is 'thus extended 'to .the

vtrunk line. =a1fcircuit is completed "i'ior the `trunk conductorl@through the winding oi relay 34L`to battery. The latter relay. on

energizingplaces vground on the multipled release trunk inthe banlrs oflocal selector :switches in which this inconiing trunk is accessible.

Now, -wlieii'the calling device of the calling 'subscriber'v'isfoperated to open the line fcircuit a number of times in accordancewith a digit of the called number, the line relay of the selector`repeater will produce a correspondingserics :of interruptions in thec.ircuit:of the line` relay 56 of the main selector F. Upon eachretraction ot' itsarinature theline relay 56 closes a circuit extendingfrom ground G11, by -wayo'f armature 91 `and its back contact, conductor137, armature 220 and its iresting Contact, yconductor 146, armature`104i and its back contact, ar-

mature 94: and its tront contact,'through "the 4winding o1e the slowacting relay 58, conductor 139, baclrcontactfand armature 215, conductor1111, armature 155 and its back contact, back cont-act andarmature 89,and

thence throughthe `winding of the vertical magnet 64 to battery. Relay58 energizes in sei-ieswitlrthe vertical magnet, and being ra slowacting relay, `maintains its armature attracted.during the operation otthe switch.

Magnet 64 operates to raise the wipers 112- 115, inclusive, step by stepuntil they are placed opposite Soinelevelfo'fbanl; contacts, in whichare terminated trunk lines leading `to I.the branch exchange secondselector switches.

Ars soon as the wipers leave theirnorinal position the spring 119 isshifted into engagement with its front contact thereby coni- .pletiiig acircuit i'or magnet GT. The operation ot this 'magnet may readily be:i-'een b retei'rino` to F i9'. 10. Uaon attractino its tn t5 :1

`armature 201', magnet 67 shifts the ott' norinal springs 116,"117'and118,-etc., into their alternate positions lwhere they lare mechanicallylocked by thespring 200. When the shattf-of the yswitch is released thepin 202 mounted thereon Awithdraws the spring'200 thereby allowing theoff normal-springs to return to their original position.

To continue, 4whenithefod normal springs battery. Relay are operated acircuit is ycompleted extending lroin ground G3, through armature v93Iand its liront contact, `arma-ture 9o and its vlront contact, armature87 and its back contact, armature 159 and its resting contact, oilnormal springs lltiiaiid thence through the windingot the interrupterrelay 59 to .59' energizes to prepare the rotary magnet circuit atarmature 100 and locks itseltl to ground at armature 99. llfhe slowacting relay 5S t'a'lls back an instant atter the impulses to thevertical Amagnet have ceased. lVhen this occurs a circuit is completedfor the rotary magnet-* extending from ground G3, by way ot armature 93rand'its front contact, armature 96 .and

its` bach contact, armature 100 and vfront contact, and through thewinding of the rotary magnet 65 to battery. Magnet 165 operates torotate the wipers 112 to 11.5, inclusive, into eiiga'geiiient `with thelirst set of contacts` in the selected level and-atthe saine time opensthe locking circuit ot relay 59iwhich deencrgizes, breaking thecircuit-of the rotary magnet which deeiiergizes also.

"When magnet 65 deenergizes it prepares a new circuit for theinterrupter relay 59 `extending from the Atest wiper 112, throughAarmature 88 and its restingcontact, baclr contact and armature160,arinature 159 and 'its bach contact, ofi' norinal springs 116, and

thence through the winding ot' relay 59 to battery. Now, it the iirsttrunk line oi this level, on the test contact of which the wiper 1121now rests, is busy al ground potential willbe present thereon and relay59 will energize over the above` traced circuit. On

energizing, l'relay 59 operates :as before to close the rotaryIii'iagnet circuit. lilagnet tloperates to advance the switch wipersinto engagement with the ot banl'contacts associated -with the nexttrunk line `and to again brcalt the circuit ot the interi'upter relay,which relay on dcenergizing breaks the rotary magnet circuit. Thisalternate yoperation oi relay V59 and magnet 65 continues unt-il aniidle trunk line is found which, it .will befassiiiiied, is the trunkline comprising ther conductors 25() to 253, in-

clusive, and which terminates in the selector H Fig. When the switchwipers are i'otated iinto engagement with this trunk line 4no groundwill be present on the test contact engaged by the wiper 112 and relay59 will not be again energized to close the rotary magnet circuit. ltwill be noticed that during the rotation of the switch in search of anidle trunl-z line the switching` relay 55 was short circuited by groundon the successive busy test contacts through lwiper 112, now, however,'when an idle trunk line is reached, the relay is no longer shortcircuited and hence it will cnergize over a circuit extending tromground G3, through armature 93aiid its front conit. Upon energizing,relay 55 opens the ver-` tical magnet circuit at armature 89, connectsground to the wiper 112 at armature i 88, prepares the circuit oit thewiper cut on relay 63 at armature 36, and completes a repeating circuitat armature 90. This repeating circuit extends from ground G1, by way ofarmature 02 and its front contact, armature 77 and its back contact,back contact and armature 72, conductor 127, armature 194 and its backContact, back contact and armature '199. conductor 121., front contactand armature 90, armature '153 and its back contact, through the windingof the slow acting series relay 61, wiper 113, bank contact 258,coinluctm' 251. ari'nature 300 and its resting contact, and through thewinding of the line relay 301 of the selector to battery. The line relay301 cnergizes in series with relay 61 and said relays 301 and 61 actuateover this circuit and conipletes a circuit in the usual manner for theslow release relay 302. This relay on energizing prepares the verticalmagnet circuit at rarmature 341 and its front contact. The actuation ofrelay 61 disables relay 63.

The calling main exchange subscriber may now operate his calling devicein accordance with the next digit of the desired number. A series ofinterruptions is thereby produced in the circuit of the line relay 56 ofthe main selector F which relay operates and at each retraction of itsarmature 92 opens the previously traced circuit for the line relay 301of the selector H. The latter relay at each deenergization sends acurrent impulse through the slow acting relay 304 and the verticalmagnet 307 in series to battery. By the operation of the vertical magnetthe selector shaft is raised step by step until the wipers 3104-313,inclusive, stand opposite the desired level of bank contacts. The slowacting relay 304 energized in series with the vertical magnet, retainsits armature,attracted throughout the `vertical movement of the switch,and upon the closure of' the 4vertical oil normal springs 314 and 315completes a circuit for the interruptor relay 305. Upon energizing relay305 prepares a circuit for the rotary magnet 308 at armature 317, and atarmature 318 establishes a locking circuit for itself. At the end of thevertical operation o1' the switch the slow acting relay 304 isdeenergized and closes the circuit of the rotary magnet, which isthereupon energized to advance the wipers 310-313, inclusive, intoengagement with the first set oli bank con tacts in the level oppositewhich they were raised. The rotary magnet also breaks the circuit of theinterrupter relay 305, which is accordingly deenergized to break thecircuit of the rotary magnet, which thereupon deenergizes also and againcloses its interrupter contact. The operation now depends upon whetherlthe test contact with Which the test wiper 310 is now in engagement isor is not busy. If this test contact is busy it will have a groundpotential on it, and the interrupter relay 305 will be energized againover a circuit which extends from the said grounded test contact, by wayof the test wiper 310, armature 320 and its back contact, theinterrupter cont-act 322 of the rotary magnet, the oi normal springs314, and the winding of the interrupter relay 305 to battery. Theinterrupting relay will therefore energize to again close the circuitot' the rotary magnet 308, which will operate to advance the switchywipers into engagement with the next set of bank contacts. Thisoperation by which the interrupter relay and the rotary magnet arealternately' energized and deenergized will continue as long as the testwiper 310 engages busy or grounded `test contacts. In the present caseit will be assumed that the truul: line shown in the drawings is thefirst idle trunk line and when therefore, the test wiper 310 arrives attest contact 325 and the rotary magnet is deenero'ized, the interruptorrelay 305 Will not e energized, but instead, the switching relay 306,which has hitherto been short circuited will be operated by currentflowing over the following path: grounded conductor 250, winding of theswitching relay 306, interrupter contact 322 of the rotary magnet, olfnormal springs 314, and the winding of the interruptor relay 305 tobattery. Owing to the high resistance of the switching relay 306, theinterrupter relay is not operated. Upon energizing, relay 006disconnects the incoming dialing conductor 251 from the winding of theline relay 301 and extends it by Way of armature 300 and its frontcontact, Wiper 311, bank contact 326, conductor 328, arma ture 366 andits back Contact, back contact and arn'iature 361, and through thewinding of line relay 350 to battery. The switching relay 306 onenergizing, also extended thel release trunk conductor 250 by way offront contact and armature 320, wiper 310, bank contact 325, conductor327, and through the winding of relay 351 to battery. This latter relayenergizes and prepares the circuit of the vertical magnet of theconnector J.

It might have happened however, that all `the trunk lines in theselected level were busy. Under these conditions the rotation of theswitch H would continue until the springs 310 and 311 were closed whichoccurs on the eleventh rotary step of the switch, being operated by thecam on the Y switch shaft in a well known manner- These springs onoperating, connect the dialing conductor 251 direct through the-windingof the line relay 301 to battery and at the same time place a busy toneon'the upper line conductor rlhis busy tone is audible to the callingsubscriber over a circuit that extends over conductor 252, bank cont-act256, wiper 11st, armature 103 and its back contact, armature 85 and itsfront contact and thence over the line of the calling subscriber. Uponhearing this tone, the calling subscriber will replace his receiver onthe switchhook knowing that ier the present he is unable to btain hisdesired connection. The replacement of the receiver at the callingsubstation initiates the release of the operated switches in a inannertobe described hereinafter.

Returning now to the operation of the system after the trunk linecomprising the conductors 323330, inclusive, has been seized; thecalling subscriber may now operate his callingV device for the nextdigit of thel called subscribers number, thereby causing the. line relay56 to again operate in response to the said impulses and repeat thein tothe line relay 350 of the connector J'. At eachl retraction of itsarmature 356, the line relay 350 completes a circuit for the verticalmagnet 372 in series with the slow acting private control relay 352,which relay maintains its armature attracted during these impulses.Magne-t 372 operates to raise the switch shaft step by step until thewipers 377-330, inclusive, stand opposite the desired level of bankcontacts. On energizing, the slow acting relay 352 completes a circuitfor the private magnet 371 at armature in multiple with relay 353. Theoperation of relay 353 is at this time without function. The privatemagnet, however, controls the sideswitch in the usual manner, and uponthe deenergization of the slow actingl private control relay 352 permitsthe sideswitch wipers to advance to their second position.

rlhe. calling subscriber may now operate his calling device inaccordance with the final digit in the called number, thereby producinga series of interruptions in the circuit of the line relay 56 whichrepeats them to the line relay 350 as before. Now, however,` this latterrelay transmits a corresponding number ofv impulses to the rotary magnet373. The circuit being traced from `ground Gl by way of armature 356 andits back contact, .armature and its front contact, through the windingof the private control relay armature 362vand its back Contact, andthrough the winding of the rotary magnet 373, and sideswitch wiperl inthe second position to battery. By the operation of the rotary magnet,in response to the impulses of current which it receives,

the switch shaft is rotated step by step, until the wipers 377-380,inclusive, arebrought into engagement with the bank contacts in whichthe desired subscribcrs line terminates, which in this case, it will beassumed, are the bank contacts 331e38t, inclusive, .in which the line ofthe subscriber at substation 1 is terminated. rlhe relay 353 and theprivate magnet 371' are energizedas before, and in case the calle-dAline is idle when the relay 352 deenergizes, the private magnetalsovdcenergizes, and the sideswitch wipers are advanced to their thirdposition.

ltY will first be assumed however, that the line-of the substation l),when called as above described, was busy. Under these condi-A tionsthere would be a ground potential on the test contacts 331and 332 whichare engaged by the test wipers 377 and 378 with the result that theprivate magnet 371 willl not deenergize when the circuit is broken forits inner winding at armature 353 but is maintained operated over a testcircuit eX- tending as follows: ground on test contact 332, test wiper378, sideswitch wiper in the second position, and through the outerwinding of the private magnet 371 to battery. Also relay a is energizedover the following circuit: grounded test Contact 381, test wiper 377,springs 365, armature 359 and its bac c contact, through the winding ofrelay 354 and the sideswitch wiper in the second position to battery. Onenergizing, relay 354 closes a locking circuit for itself and theprivate magnet independent of the test wipers 377 and 373, this circuitextending from ground G16, oil' normal springs 375, armature 364 and itsfront contacts, inner winding of the private magnet to battery and inmultiple with this last traced circuit by way of armature 359 and itsback contact, through the winding of relay 354 and the sideswitch wiperin the second position to battery. Relay 35st opens the rotary magnetcircuit at armature 362, opens the circuit of the line relay 350 atarmature 361, and places the tone from the busy machine T2 on the upperheavy talking conductor 329. When the circuit of relay 350 is openedrelay 61 in the main selector F, in

series with the dialing circuit, deenergizcs and completes the circuitfor the wiper cut on relay 63. rlhis circuit may be traced from groundG12 by way of front Contact and armature 36, armature 103 and its backcontact, and through the winding of relay 63 to battery.

The busy tone is now placed on the tone of the calling subscriber by theoperation of the relay 354 over a circuit which extends from the busymachine T2 by way of armature 363, conductor 329, bank contact 323, andwiper 312, front contact and armature Sli 321, conductor 252, bankcontact 256, wiper 114, armature 103 and its frontcontact, ar-

mature 105 and its back contact and thence through the lower winding ofthe ring cut oil' relay 62 to battery. This operation will induceacurrent corresponding to the busy tone in the upper winding of ring cut0E relay 62 from whence it flows over conductor 121 through the lowerwinding of the back bridge rela 51, off normal springs 48, back contactan armature 69, througli the condenser and thence over the lower lineconductor to the substation A and back through the upper winding ot'relay 51 to battery. This tone will inform the calling subscriber atsubstation A that the line of the subscriber at substation P is for thetime being, inaccessible, and he will replace his receiver. Thedisconnection of the various switches will be described hereinafter.

Having thus described the operation of the connector J when the calledline is busy, it will now be assumed that when the connection therewithwas attempted the line of the substation P was idle. Under thesecircumstances, when the slow acting relay 352 deenergizes at the end ofthe final series ot impulses the private magnet 371 is deenergized alsoand the sideswitch passes to the third position. By the advance of thesideswitch wipers to their third position two circuits are closed inmultiple. One extending from ground G17, sideswitch wiper in the thirdposition, through the test wiper 378, test contact 382, private normalconductor 385. springs 386, conductor 387, the winding of switchingrelay 407 of the lineswitch C', and the winding ofthe stepping magnet tobattery. In parallel with this circuit one is also closed for the busylamp 452 thereby notifying an operator who has access to the line of thesubscriber at substation P that this line is now busy. The current flowin this circuit serves to energize the switching relay 407, the steppingmagnet remaining deenergized, and the line conductors 405 and 406 arethereby disconnected from their normal battery and ground connections inthe lineswitch C. It should be here mentioned that when relay 407energizes as described above it. is prevented from completely attractingits armatures by reason ot a mechanical interlocking device controlledby the armature of the line relay 408 when in normal position. Ground atG, of course, also extends to multiples of test contacts 381 and 382 inother connector switches both incoming and local which 4have access tothe line of the substation P in order to render this line busy. lVhenthe sideswitch steps to the third position another circuit is alsocompleted in multiple with the above for the wiper cut on relay 355 inan obvious manner. On energizing, relay 355 prepares the ringing circuitat armatures 367 and 368, and at armature 366 opens the circuit of theline relay 350. f As before, as soon as the circuitto the line relayv350 is broken the slow acting series relay 61 in the main selector Fdeenergizes. A circuit is thereby completed gizes a short intervalafterwards. During` this interval a distinctive tone from the tonemachine T is placed on the calling subscribers line conductor therebynotifying him that his call is proceeding satisfactorily. Relay 63 uponenergizing, completes the ringing circuit for the called subscriberstelephone which extends from theungrounded pole of generator V, overconductor`245, conductor 145, back contact and armature 107, armature111 and its front contact, wiper 115, bank contact 257, conductor 253,armature 260 and its front contact, wiper 313, bank Contact 324,conductor 330, armature 368 and its front contact, wiper 380, bankcontact 384, line conductors 393 and 401 of the substation P, throughthe ringer and condenser of the said substation, line conductors 400 and390, bank Contact 383, wiper 379, front contact and armature 367,conductor 329, bank contact 323, wiper 312, 'front contact and armature321, conductor 252, bank contact 256, wiper 114, armature 108 and itsfront contact, armature 105 and its resting contact, and thence throughthe lower winding of the ring cut off relay 62 to battery. This ringingcurrent also causes an induced tone in the upper winding of the ring cutofi' relay which is audible to the calling subscriber, thereby notifyinghim that his call is proceeding satisfactorily. The ringing of thecalled substation P will continue intermittently in the ordinary manneruntil the subscriber thereat removes his receiver. When this occurs acircuit for direct current is completed over the previously vtracedringing circuit through the switchhook springs, transmitter, andreceiver of the called substation for the ring cut oli' relay 62, which,while it is adjusted not to respond to alternating current,will operateover this circuit. On energizing, relay 62 disconnects the ringingcurrent from the called line at larmature 107, at the same time.connects the talking circuit to the windings of the back bridge relay 51at armatures 105 and 107 and their front contacts, and locks itselfenergized at armature, 106 and its front contact. A circuit is nowcompleted extending from ground G13 off normal `springs 118 and itsworking contact, front contact and armature 106, conductor 121', throughthe lower winding of the back bridge relay 51, working contact of offnormal spring 48 and the said spring, front contact and armature 107,and then over the previously traced lll),

ringing circuit back to wiper 114, armature 108 and its front contact,armature 105 and its front contact, working contact of oil' normalspring 4:9 and the said spring, and through the upper winding of thebaclr bridge relay 51 to battery. Relay 51 will thereforeenergize,completing a circuit erttending trom ground G4 by way otarmature and its trent contactspring'117 of key K and its restingContact, conduct-or 132, armature 200 and its resting contact, conductor131, resting contact ot spring 118 and the said spring, andthrough thewinding ot the slow actin(y relay 52 to battery. Relay 52 will attractits armatures and at armature 7 3 complete the circuit ot relay 53 andat armature 76 place ground on conductor 36 extending throughl thewinding of relay 25 to battery. On energizing, thislatter relay.reverses the connections of the line relay 56 with regard to the trunkconductors 26 and 27 thereby reversing the battery back to the callingVline vfor any desired purpose. The energization ot relayv 53 simplyprepares the f operating circuits of the auxiliary selector G. y'llhecalling and called subscribers may now converse over the heavyconductors in theusual manner.

When the conversation is completed the connection may be released by thehanging up of the receiver at the calling' substation. Relay 56 willtherefore ileenergize opening` the circuit ot' the slow acting releaserelay 57, which deenergizes also. This latter re` lay on decnergizingremoves ground trom the release trunk 'conductor and at the same timecloses circuit t'or the release magnet extending from ground G by way ofarmature 93 and its back contact oli' normal springs 117, and throughthe winding ot the release magnet 66 to battery. r1`he switch F will beimmediately released by the energization ot magnet 66 and as theholdingcircuit tor the slow acting release relay 351 ot' the connector Jand the switching relay 306 of the selector H has been opened. by thedeenergization oit relay 57 each ot these relays will accordinglydeenergize. tending from ground G2, by way of armature 399 and its backContact. oli normal springs 374, and through the winding otl the releasemagnet 369 to battery, and rel.fcompletes a circuit extending from byway ot' armature 308 and its back contact, back contact and armatureSL10, armature 341and its back contact, ott' normal springs 4315, andthen through the windingl et the release magnet 342 to battery. lttag-vnets 869 and '312 will operate to restore their respective switches totheir normal position. Thusnin the above described manner all theswitches will beirestored to normal.

Let us now assumethat the calling` subscriber who has directed. theextension of the Dtelay 351 completes a circuit err;

previously described connection, desires to tall; with some othersubscriber in the branch exchange. In order to do this he will merelydial the local branch exchange number ot that subscriber, therebyoperating` the auxiliary selector G to select an idle branch eX- changesecond selector, after which the call will proceed in the ordinarymanner.

This operation will now be described. lli'lhen the calling device of thesubstation A is operated a series ot' interruptions is produced in 'thecircuit ot the line relay 56. At each retraction ot its armature 91, acircuit is con pleted extending troni ground G11, by way of armature 01and its baci; contact, conductor 137, armature 220 and its bach contact,conductor 1&6, armature 104- and its resting Contact, armature 94 andits trent contact, armature 97 and its back contact, conductor 1110,through the winding ot' slow acting series relay 171, armature 281 andits baclr contact, armature 211 and its back Contact, and through thewinding ot' the ycrtical magnet 177 to battery. will be noticed thatthis circuit was also operative when the main selector was operated inthe original connection but under these conditions the series relay 58is adjustH ed to'pull up lirst breaking the above traced circuit atarmature 97, whereupon it was then ineti'ective. Relay 56 also completesanother circuit. at each retraction ot' its armature 02 ent ,riding*from ground G by way ot armature and its back contact, front contactand arn'iature 95, conductor 138, and thence through the winding ollslow acting relay 170 to battery. This relay energiyes, and at armature213 places fijround on conductor 136, and at armature and its troutcontact places ground on conductor 151, extending by way ot armature andits trout contact, oli' normal springs 117, and through the winding ofrelease magnet 66 to battery. lilagnet 06 operates to loci; itseli toground on conductor 13 at armature 157, to open the operating andrepasting circuits ot' the main selector F and 'to restore the saidswitch to its normal position. The slow acting series relay 171cnergizes in series with the vertical magnet 177 and opens the operatingcircuits ot the main selector l? at armature 215. Magnet 177 operates inthe usual manner to step the wipers 2351-238, inclusive, opposite somelevel otbanlr contacts in which trunk lines leading to selectors areterminated. Upon the wipers leaving their normal position the circuit otthe oli normal magnet 160 is completed and it operates to shift thesprings 2110, 241, 2*-1r2, 2-15, and 2416 into their otln normalposition in a similar manner to magnet 67. A circuit isthereby completedex-` tending trem ground by way of armature 93 and its front Contact,conductor 36. conductor 123, armature 216 `and its trout contact,armature 234 and its back contact, olf normal springs 240, and thencethrough the winding of relay 172 to battery. Relay 172 energizes overthis circuit locks itself to ground at armature 218 and its frontcontact, by Way ot the interrupter springs 181 ot' the rotary magnet178, and at armature 219 and its front contact prepares the rotarymagnet circuit. The release magnet 66 of the main selector F remainsenergized until the slow acting relay 17() deenergizes at the end of thevertical movement of the switch Gr, having maintained the operatingcircuits of the main selector F open. After the impulses to the verticalmagnet 177 cease, the circuit through the winding oi relay 171 is openat back contact ot armature 91, relay 171 therefore deenergizes after aninstant and completes a circuit to the rotary magnet 178. Magnet 178operates to step the Wipers 235-238, inclusive, onto the first set ofbank contacts in the selected level and also to open the locking circuitot the interrupter relay 172 which deenergizes and opens the circuit ofthe rotary magnet which deenergizes also. Now if the selector switchassociated with the tiret set of bank contacts is busy a groundpotential will be present on the test contact engaged by the test Wiper235. Then as soon as magnet 178 deenergizes the circuit of relay 172will again be closed from ground by Way of the said test Wiper, armature299 and its back contact, interrupter springs 181, and then over thepreviously traced circuit through the Winding of relay 172 to battery.The relay 172 will again energize therefore to close the circuit of therotary magnet at armature 219 and its front contact. The rotary magnetoperates as before to step the Wipers 235-238, inclusive, on to the nextset of bank contacts and to open the locking circuit of yrelay 17 2which deenergizes opening the rotary magnet circuit which deenergizesThis alternate operation of relay 1.72 and the rotary magnet 178continues until. an idle trunk is found which We Will assume, is the4trunk line comprising conductors 262. 263, 264, and 265, the testcontact 268 of which will be ungrounded and hence there will be nocircuit for relay 172. The switching relay 169 which has hitherto beenshort circuited by the ground on the various test contacts will no7 beenergized as there is no` ground potential on the test Contact ot' anidle trunk line. The circuit for the energization of relay 169 extendsfrom ground on conductor 123 through the Winding ot relay 169, springs181, thence over the previously traced circuit and through the Windingof relay 17 2 to battery. Relay 169 is of such high resistance that italone will energize over the above traced circuit thereby opening thevertical magnet circuit at armature 211, placing ground on the relinerelay 350 of the selected selector I.

This circuit extending from ground Gr11 by way of armature 92 and itsfront contact, ari'nature 77 and its resting contact, back contact andarmature 72, conductor 127, armature 1,94-and-its back contact, backcontact and armature 199, front contact and armature 210, armature 233and its back contact, through the Winding of slow acting series relay173, wiper 236, bank contact 269, conductor 263, armature 355 and itsresting contact, and through the Windingof the line relay 350 of theselector 1.

Relays 173 and 350', Will energize over the circuit, relay 173completing the circuit of slow acting relay 174 at armature 221, andrelay 350 completing the circuit of' the slow acting rcleaserelay 351.The calling subscriber at substation A may novs7 operate .his callingdevice for the next digit of thedesir-ed number thereby 'producing aseries of interriiptions in the circuit of the .line relay 56 oi? themain selector .F Which operates to repeat them to the line relay 350 ofthe selector I over the previously traced circuit. The line relay 350responds thereto, to control the operation ot the vertical magnet 356which operates to step the Wipers 359-362, inclusive, opposite thedesired level of bank contacts. The selector then rotates to find anidle trunk line in identically the same manner as the selector Hoperated, which operation Was described fully hereinbefore.

Upon an idle trunk being selected which, we l will assume, is the trunkline comprising conductors 379-382, inclusive, the switching relay 354'will energize in the usual manner in series With the interlnpter relay353. On its energization, relay 354 disconnects the incoming dialingconductor 263 from the Winding of the line relay 350 and extends itthrough armature 355 and its front Contact, Wiper 360, bank contact376', conductor 380', armature 425 and its resting contact, back contactand armature 426 and then through the Winding of the line relay 400 ofthe connector K to bat tery. The switching relay 354 also extendstherelease trunk conductor 262 by Way ofI front contact and armature357', test wiper 359', bank contact 375', conductor 37 9', and throughthe Winding of the slow acting release relay 401 to battery.

The calling subscriber may now operate his calling device for the lasttwo digit-s of his desired number thereby causing the line relay 56 ofthe main selector D to repeat these impulses to the line relay 400 ofthe connector K in the usual manner. The line relay 400 controls theoperation of the connector to connect with the desired line. If thisline should happen to be busy then the ductor 881 at armature 419.8 andat armature 426 opening the circuit to the line relay 400 or" theconnector K. Pllhe busy tone is audible to the calling subscriber over acircuit similar to the one hereinbelore traced, and upon hearing thistone the calling subscriber will hang up thereby releasing the operatedswitches in a manner similar to that her-einbetore described.

Assuming no-w that the second called subscribers lin-e is idle, then assoon as relay 4.05 energizes the dialing conductor is opened as beforeat armature 1125, and the ringing circuit is prepared at armature 1127and 129. As before described, as soon as the circuit to the line relaylOO is broken the slow acting series relay 17 3 deenergizes completingthe circuit for the wiper cut on relay 176 and at the same time placesthe connector cut on tone in the calling subscribers line for a shortinterval noti 'ying him ot the operation. Upon relay 176 energizing, theringing circuit tor the called subscriber is completed from thegenerator V and this current flows over a circuit similar to when thesubscriber at substation P was signalled, through the ringer of calledsubstation back through the low-er winding ot the ring cut oil relay175. llfhen the subscriber answers the ring cut off relay energizes overthe line circuit and operates to cut od the ring and complete thecircuitoil the bach bridge relay 165 which also energizes over a circuitincluding the called subscribers line loop. Upon energizing., .relay 165closes circuit tor the slow `cting relay 166 which relay operates toprepare the operating circuits of the main selector F, completes thecircuit oit the slow acting relay 167 and also places ground onconductor 128 which extents througl'i the winding ot' the reversingrelay to battery. rlhis latter relay operates as before, to reverse thebattery over the trunk line tor any desirable purpose. Conversation maynow be carried on between the two parties over the heavy line cnductors.Alfter this is terminated the connection may be released as beforedescribed by the calling subscriber replacing his receiver ontheswitchhoolz.

rlhis passing ot 'the callv by the calling subscriber may be continuedindefinitely as long as desirable each time releasing the called partyin the connection upon the first digit of the nef-:t subscribers numberif the called party remains on the line. lt however, the calledsubscriber hangs up irst a circuit tor the release magnet ot theselector which is then in use is effective. kAssuming the main tor l? tobe in use; when the called subiber replaces his receiver on theswitchbridge relay 165.

hook the circuit ot the back bridge relay 51 is opened which relaydeenergizes sending` an impulse of current at armature to the slowacting yrelay 5&1 which energizes. A circuit is now effective extendingtrom ground G1, ottl normal spring 242 and its resting contact,conductor 148, front contact and armature 82, armature 74 and its backcontact, oli normals rings 117, and through the winding ot releasemagnet- 66 to battery. Magnet 66 operates, opening the operatingcircuits ot the main selector as bei'iore, and restores the switch F tonormal. Now, it' the calling subscriber should pass the call he willoperate the main selector F again as in the case lirstdescribed, all theapparatus being now in its original position.

1t will now be assumed that the second called subscriber' called throughelement G finds that it is necessary to call another sub- -1 scriber forthe calling party. Under these conditions the second called party willoperate his calling device 'for the 'local subscribers number producinga number of series of interruptions in the, circuit of the back ilillienthe second called subscriber operates his calling device tor the iii-stdigit ot the local number the hack bridge relay 165 responds to theinterruptions in its Iline circuit and at each retraction of itsarmature 193 completes a circuitk as follows:

`from ground G14 by way ot armature 193 no etlect. Relay 185 alsoenergizes in parallel with the relay 168 and -being slow act-- ingrelay, maintains its .armature attracted throughout each series ofimpulses serving to open the circuit to the line of the callingsubscriber thereby preventing the dial impulses from causing him lanyannoyance. The slow actingseries relay 58 also energizes in cries withthe vertical magnet circuit and maintains its armature attractedthro-ugl-iout the vertical movement ot the switch. Magnet 611 operatesbefore, to step the wipers 1124.15, inclusive, opposite some level ofbanlr contacts in which terminate trunk lines leading to selectorswitches. As beiore described, upon the wipers leaving their normalposition the oli normal springs operate and a circuit is completed forthe interruptor relay 59, which energizes, establishes a locking circuit'for itself, and prepares the vrotary magnet circuit. At the end of thevertical movement of the switch, relay 58 deencrgizes completing thecircuit of the rotary magnet 65 which operates to open the lockingcircuit of the interrupter relay 59 and to r0- tate the wipers 112-115,inclusive, into engagement with the first set of bank contacts in theselected level. The interrupter relay, of course, deenergizes, breakingthe circuit of the rotary magnet which also deenergizes. The trunkselecting operation will go forward in the manner previously explaineduntil a trunk is found terminating in an idle selector switch which itwill be assumed is the trunk line compris-ing the conductors 250, 251,252, and 253. Vhen the switching relay energizes, upon an idle trunkline being found, a repeating circuit is completed extending as follows:ground G11, armature 92 and its front contact, armature 7 7 and its backcontact, back contact and armature 72, conductor 127, armature 194 andits front contact, front contact and armature 199, conductor 121, frontcontact and armature 90, armature 158 and its back cont-act, through thewinding of the slow acting relay 61, wiper 113, bank contact 258,conductor 251, armature 800 and its back contact, and thence through thewinding of the line relay 301 of the selector H. The operation of thisselector and the connector operated in response to the succeeding digitsof a third calle-d subscribers number will, of course, be identical withthat hereinbefore described. Should the second called party discoverthat he made an error in calling one of his numbers before sending thelastdigit or during its transmission he may replace his receiver on theswitchhook thereby breaking the. cir cuit of the back bridge relay 165which deenergizes. A circuit is then completed extendfrom ground G13,off normal spring 118 and its working contact, armature 109 and its backcontact, conductor 150, armature 203 and its front contact, back contactand armature 196, conductor 180, off normal springs 117, and through thewinding of the release magnet 66 to battery. Magnet 66 voperates in theusual manner to restore the ymain selector to normal after which thesucceeding switches will be restored by their respective releasemagnets.

However, if the second called subscriber completes the connection to thethird called subscribers line and should then desire to release in casethe line is busy or the party called dont answer he may do so by dialingthe digit 1, thereby producing another interruption in the circuit ofthe back bridge relay 165 which operates to send an impulse of currentto the slow acting relay 168 in the usual manner. A circuit is theneffect-ive extending as follows: from ground G15 by Way of armature 192and its front contact, armature 205 and its front contact, conductor151, armature 110 and its front contact, (relay 63 now being energized),off normal springs 117 and through the winding of the release magnet 66to battery. Magnet 66 will operate and the switch F will then berestored to its normal position. The operated switches will then berestored to normal in a manner hereinbefore described.

It may sometimes happen under certain conditions that an impulse ofcurrent is sent to the vertical magnet of one of the dual switches. Itwill be assumed that an impulse of current has been sent to the verticalmagnet of the main selector F. Under these conditions magnet 611 willoperate stepping the shaftup one step thereby causing the springs 1,19to operate and upon the deenergization of the slow acting series relay58 a circuit is completed extending from ground. G22, spring 119 and itsfront contact, back Contact and armature 98, off normal springs 117, andthrough the winding of the release magnet 66 to battery. Magnet 66 willoperate and the switch F will be restored to normal. Therefore, eventhough the vertical magnet does operate one step the corresponding dualselectorl will be automatically restored to normal. that a subscriberwho has connected over a trunk to the ldual switches may by dialingdigit 1 four times restore which ever one of the dual switches next tobe used to its normal condition because if the said one of the switchesis normal it will step to the first level and release four timesresponsive to the four digits. If in an operated position the selectorthen seized and thereafter a connector will be operated, and finally acircuit will be completed for the release magnet of the operated dualswitch in response to the next digit over` one of the release circuitsherein described so the said selector' and con- It also follows nectorwill also be restored. Any subsequent digits 1 sent after therestoration of the switches will operate the restored dual switch andthereupon restore it. That is, if four digits 1 are not required to linkthe connector to the called line terminals and restore it, the extradigits 1 sent will have no linking effect as the dual switch elementwill operate and release idly for each extra digit 1.

lt will now be assumed that the second called subscriber aftercompleting the setting up of the connection yto a third partys line doesnot wish to hold the line until that party answers. He will thereforereplace his receiver on the switchhook, the circuit of\ the back bridgerelay 165 is thereby broken and on its deenergization sends an impulseof current to the slow acting relay 168. A circuit is now effectivefora'elease magnet 179 of the auxiliary selector G extending from groundG13, through ofi' normal Spring 118 and its working Contact, armature109and its front Contact, conductor 1119, armature 204 and its frontcontact, armature 197 and its back contact, off normal springs 241,

f long as desired.

and then through the winding ot the release magnet 179 to battery. Themagnet 17 9 will operate to restore the auxiliary selector G to normalafter which the switches K and I that maintainedv the connection to thesecond calledsubscriber will be released by 'the operation of theirrespective release magnets. In the meantime the signalling' ot the thirdcalled subscriber will be going on and upon an answer being obtainedconversation between the original calling and third called parties maytake place over the same switches that were operated in the lirst casedescribed. After the conversation is terminated the release will takeplace in the usual manner upon the subscribers replacing their receiversupon the switchhooks.

This third called subscriber may pass the call to a fourth subscriber ina manner similar to that above described except that the back bridgerelay 51 will be operated in response to the various digits to controlthe operations of the auxiliary selector and the succeeding switches.

It will thus be seen that this passing of a call by either the callingor called subscriber may go on indelinitely and in each case only thetwo subscribers are in communication at once. It may be desirablehowever to arrange this system so that the three subscribers may remainon the connection for a conference, in this case the key K associatedwith the dual switches is operated by some person say the exchangeattendant. Now when the Acall is passed by a called subscriber the threeparties may remain in on the connection. The operation ot the system inthis case will now be briefly described.

For the purposes of this description it will be assumed that a callingmain exchange subscriber at substationrhas called abr-anch exchangesubscriber at substation P by means ot' the main selector F and thesucceeding switches in a mann-er similar 'to that hereinbeforeexplained, and that the subscriber thereat has responded and hasextended the connection to the line' of another branch exchangesubscriber such as the .one at substation O through the medium of theauxiliary selector G and the switch-es I and K. The subscriber at thesubstation O will be rung in the ordinary manner and that subscriberupon removing' ihis receiver from the switchhook will stop the ringingIope"ation and complete the circuit ot the back bridge relay 165 asdescribed hereinbefore. Upon energizing, relay 165 will close thecircuit yot the slow acting relay 166 through the key spring 120 and itsworking contact and hence the release circuit through the contacts ofthe slow acting relay 52 is inettective. The three parties may nowconverse as It' atany time one of the branch exchange subscribers, theone at substation P for example, should desire to tall; to the callingsubscriber alone he will simply operate his calling device for the digit1, thereby producing one interruption in the circuit or' his back bridgerelay 51. Upon the retraction of armatur 70, slow-releasing relay 54will actuate, so when armature 71 retracts a circuit may he traced fromground G5 by way of armature 71 and its Yliront contact, armature 84 andits front contact, conductor 135, armature 229 and its front contact,oli normal .spring 241, and thence through the winding of the releasemagnet 179 to battery. Magnet 179 operates to restore the auxiliaryselector G to normal a-tter which the selector l and connector K will bereleased. It will be seen that the subscriber at substation O could havereleased the subscriber at substation P in a similar manner bydialing 1. This circuit would extend 'trom ground G15, by way ofarmature 192 and its front contact, armature 205 and its front contact,conductor 151, armature 110 and its front contact, ott normal springs11T and thence through the winding or the release magnet 66 to battery.ln this manner the system may be arranged so that the three subscribersmay remain on the connection and at the same time providing means sothat ir" it becomes necessary or desirable for one of the parties toconverse secretly with the party calling over the trunk from the mainexchange the third may be released. It will be seen that any digit mightbe dialed in place of 1 to release for the reason that the operatedswitch will release upon the first impulse as above described and thenthe release magnet will lock up through its armatures opening theoperating circuits ot' that switch. This locking circuitot the releasemagnet will be cll'ective until all the `impulses ot' the digit calledto release have ceased tor 'the reason that one slow acting series relaywill be energized locking 'the release magnet in an obvious manner.

Under certain conditions it mightbe desir-able to arrange groups oitelephones under one number and it' one of these were busy the otherwould be selected automatically. The connectors J and K have also beendesigned to serve this class of subscribers. To arrange the connector Jto serve this class oit subscribers the tie between the two testv .or.private bank contacts such as 381 and 382 is omitted in all except theprivate contacts o't the last telephone in the group. Now when thisconnector under the control of a calling subscriber attempts to connectwith the first telephone in the group and this being busy, ground willonly be present on the lower test contact. A circuit is now completedfrom the said grounded test contact by way of the test wiper 37S,sideswitch wiper in the second position and through the outer windingoli the private

